1. Field of the Invention
The present invention relates generally to the removal of gold films from gold-plated articles and, more particularly, to the stripping of gold films without oxidizing or dissolving the gold.
2. Discussion of the Prior Art
U.S. Pat. No. 3,242,090 to Grunwald describes prior methods of stripping gold such as electrolytic procedures wherein the gold-plated article is used as an anode in an aqueous solution of sulfuric acid, and chemical procedures wherein a solution of a cyanide and an oxidizing agent such as hydrogen peroxide is used to oxidize and dissolve the gold. The method claimed by Grunwald involves the improvement of using certain complex cyanides, especially complex tetracyanide anions, in combination with suitable oxidizing agents.
Generally, gold films are removed from coated articles only by dissolving the metal in strong oxidizing media such as aqua regia, a mixture of hydrochloric and nitric acids which generates active chlorine, or in strong complexing cyanide solutions in combination with oxygen. The above-described media develop noxious fumes, are poisonous and hazardous, and are therefore undesirable for stripping gold films under production line conditions. As an alternative, a gold film may be removed by wiping it from the substrate. However, this technique is effective only with fresh gold films prepared by electroless deposition and, in addition, recovery of the gold is difficult.